1. Field of the Invention
Example embodiments relate to a magnetic memory device, and more particularly, to a magnetic memory device where data bits are stored in an array. Each data bit may include a magnetic domain and may be moved according to magnetic domain motion. Example embodiments also relate to methods of reading and writing to the magnetic memory device.
2. Description of the Related Art
A magnetic random access memory (MRAM) is an example of a non-volatile magnetic memory and may operate based on a magnetic resistance effect, which takes advantage of spin-dependent conduction peculiar to a nano-magnetic material. An MRAM may operate based on the giant magnetoresistance (GMR) effect or the tunnel magnetoresistance (TMR) effect manifesting as spin. Spin is a degree of freedom of an electron and may have an influence on electron delivery.
The GMR effect manifests as a resistance difference observed in an arrangement of ferromagnetic materials having a non-magnetic material interposed therebetween. The resistance difference results from an orientation of magnetization directions in a ferromagnetic material/metallic non-magnetic material/ferromagnetic material arrangement. The TMR effect occurs in an arrangement of ferromagnetic materials having an insulator interposed therebetween. The TMR resistance of the arrangement may allow current to more easily flow through the arrangement if two ferromagnetic materials have the same magnetization direction as compared to a case in which the two ferromagnetic materials have different magnetization directions.
Because a conventional MRAM based on the GMR effect generally has a relatively small resistance difference caused by a magnetization direction, a large voltage difference generally cannot be achieved. Also, because a conventional MRAM has the disadvantage that a size of a metal oxide semiconductor field effect transistor (MOSFET) that may be combined with a GMR layer in order to form a cell should increase, research pursuing commercialization of an MRAM using the TMR layer instead of a GMR layer is more actively being pursued.
A conventional MRAM may include a transistor, which is a switching device, and a magnetic tunnel junction (MTJ) cell in which data may be stored. Generally, the MTJ cell may include a pinned ferromagnetic layer having a pinned magnetization direction, a free ferromagnetic layer whose magnetization direction may be parallel or anti-parallel to the pinned magnetization direction of the pinned ferromagnetic layer, and a non-magnetic layer located between and magnetically separating the pinned ferromagnetic layer and the free ferromagnetic layer.
However, because a conventional MRAM having MTJ cells only stores one-bit data per cell, the conventional MRAM is limited with respect to increasing data storage.